Chloroplast genes are transcribed by an RNA polymerase containing plastid-encoded subunits homologous to the α, β and β′ subunits of E. coli RNA polymerase. The promoters utilized by this enzyme are similar to E. coli σ70-promoters consisting of −35 and −10 consensus elements (G. L. Igloi and H. Kossel, Crit. Rev. Plant Sci. 10, 525, 1992; W. Gruissem and J. C. Tonkyn, Crit. Rev. Plant. Sci. 12:-19, 1993) Promoter selection by the plastid-encoded RNA polymerase is dependent on nuclear-encoded sigma-like factors (Link et al. 1994, Plant promoters and transcription factors, Springer Verlag, Heidelberg, pp 63-83). In addition, transcription activity from some promoters is modulated by nuclear-encoded transcription factors interacting with elements upstream of the core promoter (L. A. Allison and P. Maliga, EMBO J., 14:3721-3730; R. Iratni, L. Baeza, A. Andreeva, R. Mache, S. Lerbs-Mache, Genes Dev. 8, 2928, 1994, Sun et al., Mol. Cell Biol. 9:5650-5659, 1989). These factors mediate nuclear control of plastid gene expression in response to developmental and environmental stimuli.
The existence of a second nuclear encoded polymerase transcription system in plastids has been demonstrated. However, the relevant nucleic acid sequences required for transcription initiation comprising the novel regulatory elements of this system have yet to be elucidated. It is an object of the present invention to provide these novel genetic elements. Incorporation of these regulatory elements into specific plastid directed DNA constructs enables greater flexibility and range in plant species available for plastid transformation, and facilitates ubiquitous expression of foreign proteins and/or RNAs and are useful in non-green plastids.